Look out for 2nd & 3rd conditional unreal sentences in the text. 
The end of the world could’ve happened yesterday. What would you have done if you had known only a few hours before impact? Ok, so this is an exaggeration. The asteroid 2005 YU55 safely passed the Earth at 11:28pm on Tuesday. It is 400metres in diameter and last night it was closer to the Earth than the moon. Maybe it was because I had just watched the film Melancholia (about a planet colliding into Earth with only a few hours warning), but I kept looking out of the window until 11:30pm. If the world was going to end, I wanted to know about it! So the next day I wondered, “If I had seen the asteroid coming to earth, what would I have done in my last few hours?” I know, quite a morbid thought on a Wednesday morning. Anyway, to be honest, I’m quite a laid-back person so I wouldn’t have wanted to panic. I was also lucky because I was already with one person I loved, so I think I would’ve called my family and just watched the world end from my balcony. What about the other teachers? Sarah, a relatively new teacher, was nice enough to respond to the question without thinking I was a weirdo: “If there had only been a few hours notice, I would’ve called all my friends to come over for one big end-of-the-world party!” Roger, a distinctly older teacher replied: “I was washing the dishes a few hours before the asteroid passed. If I’d known it was going to hit Earth at this moment, I might’ve finished the washing-up. It depended on if I had wanted to die knowing that I had finished my chores.” Bren said about last night: “If an asteroid was on target with the earth, I would make a bad joke like, “Well, don’t worry about it. It’s not the end of the world, is it?” And then I’d think about possibly asking for … from the nearest babe.” Maria, my current co-teacher, responded with: “That was never going to happen. But if it had, I would’ve taken the first flight to Africa to spend my last hours in the country I love the most – Mali.” Even if she’d had 12 hours warning, she probably couldn’t have taken a flight at such short notice anyway. Good thing that this never happened! Apparently the next time an asteroid gets this close to Earth will be in 2029 – and it’ll be the same one. So you have a long time to think, “What would you do if it was going to hit the world?”
2nd Conditional: If + past simple / past continuous, subject + would/wouldn’t + infinitive
Use to talk about hypothetical situations in the present and future. You can use might or could instead of would for possibility
- If the world was going to end, I would want to know about it
- If an asteroid was on target with the earth, I would make a bad joke
3rd Conditional: If + past perfect, subject + would/wouldn’t / could/could’ve / might + have + past participle
We use to talk about hypothetical situations with a past consequence You can use might have or could have instead of would have for possibility
- If there had only been a few hours notice, I would’ve called all my friends to come over for one big end-of-the-world party
- If I’d known it was going to hit Earth at this moment, I might’ve finished the washing-up
- If she’d had 12 hours warning, she probably couldn’t have taken a flight at such short notice anyway.
